the costco version of the Shark PowerDetect is not a duo head at all. Simple single roller design. Notably cheaper $150 range, but how much will you lose compared to the IP3251 new duo roller head??
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I just bought one of these from Best Buy for an effective $360 ($400 sale and extra 10% cardmember appreciation). I hadn't seen many reviews on it, probably because it's so new, so I was nervous. No need to be nervous: it is amazing!
I thought all of the fancy Detect things would just be gimmicks, but they really do make a difference. Dirt detect helps battery last a lot longer; I vacuumed hardwoods and area rugs for over a half hour and it was flashing 1 bar of battery, but still going. Edge detect is incredible because it kicks on and really does pull in dirt off the baseboards in ways no other vacuum has for me. Even light detect is nice because the light is always on the show dirt in front of the vacuum, but light detect also helps light up the room if it is dark.
I've had two Shark Navigator LiftAways. When I bought the second one, I noticed that they kept the general design the same over the years but improved the engineering on a few things (like adding structural fins to plastic parts prone to breaking) so I've been a Shark fan since noticing that. My previous cordless is a Bissell ClearView XR which was neat, but not super effective.
My area rugs feel like new. So much nasty dust was pulled out of the fibers. And the fins of the roller fluffed up the fibers. Seriously my rugs haven't felt this soft in years. This vacuum is amazing.
100% do yourself a favor and get the Clean & Empty version. Having a base to put the vacuum in which pulls all the hair and dust without any of it going into the air is such an improvement. With the Bissell, I'm always holding my breath when I empty it, my garbage can gets dusty, often I spill on the floor by accident. With this new Shark, it sucks it all down (base, then the vacuum does a little rev, then base again quickly) and I supposedly should only need to empty once a month, which means it is going to the outside bin no problem. Oh, and it charges from that base too so it's always ready for you.
Can't recommend this vacuum enough! Hope this review helps; I would've appreciated finding one before purchasing so I wasn't nervous for no reason!